Ghost on my video?

I am really fucking confused right now. I post videos playing guitar and music on TikTok on a private account. I recorded a new one and went I went to watch it I heard a woman’s singing along with mine. At first I thought maybe it was just a video glitched and it accidentally played at the same time I was recording but during the chorus the singing hummed the exact melody of the song. WHAT THE FUCK? I was outside ALONE recording this with literally nobody around and this is something I would have heard. Anyone got a good explanation?